#include<bits/stdc++.h>

using namespace std;

int main() {
    double a, b, c;
    cin >> a >> b >> c;
    if (a <= 0 || b <= 0 || c < 0 || a + b <= c || b + c <= a || c + a <= b) {
        cout << "Something wrong~" << endl;
        return 0;
    }
    double s = (a + b + c) / 2;
    double area = sqrt(s * (s - a) * (s - b) * (s - c));
    cout << fixed << setprecision(3) << area << endl;


    return 0;
}
